It has been found that a family of protein kinases, namely cyclin-dependent kinases or CDKs, play a central role in the cell division cycle. Deregulation of CDK activity has been documented in a number of human primary tumors and tumor cell lines, see Kamb, A. Cyclin-dependent kinase inhibitors and human cancer, Curr. Top. Microbiol. Immunol., 227: 139-148, 1998. It stands to reason therefore that preferential inhibition of these kinases would be key in the treatment or prevention of proliferative diseases.
Paullones represent a novel class of small molecule CDK inhibitors. They are a family of benzazepinones with promising antitumoral properties. Recently, paullones have been described as potent ATP-competitive inhibitors of the cell cycle regulating cyclin-dependent kinases. They are also indicated as potent inhibitors of glycogen synthase kinase-3B (GSK-3B) and the neuronal DCK5/p25, see Leost et al., Paullones are potent inhibitors of glycogen synthase kinase-3B and cyclin-dependent kinase 5/p25, Eur. J. Biochem., 267: 5983-5994, 2000.
Several chemical agents that are selective CDK inhibitors are known or have been developed such as lactones (e.g. butyrolactone I), flavonoids (e.g. flavopiridol) and purine derivatives to name a few. Some have shown antiproliferative activity for colon and pancreatic carcinoma cell lines. Flavopiridol has entered clinical trials as an anticancer agent. Paullones have been compared to these known compounds and have been found to be equipotent with respect to CDK inhibition.
One lead stucture alsterpaullone (9-nitro-7,12-dihydroindolo-[3,2-d][1]benzazepin-6(5H)-one, has been derivatized at both the lactam and/or indole portion in an effort to increase anti-tumor activity. Although the CDK inhibition activity remains high, the antiproliferative activity remains poor throughout the paullone family. One explanation could be the insolubility of these compounds.
Over the years, several methods of administering biologically-effective materials to mammals have been proposed. Many medicinal agents are available as water-soluble salts and can be included in pharmaceutical formulations relatively easily. Problems arise when the desired medicinal agent is either insoluble in aqueous fluids or is rapidly degraded in vivo. Paullones are often especially difficult to solubilize.
One way to solubilize medicinal agents is to include them as part of a soluble prodrug. Prodrugs include chemical derivatives of a biologically-active parent compound which, upon administration, eventually liberate the parent compound in vivo. Prodrugs allow the artisan to modify the onset and/or duration of action of an agent in vivo and can modify the transportation, distribution or solubility of a drug in the body. Furthermore, prodrug formulations often reduce the toxicity and/or otherwise overcome difficulties encountered when administering pharmaceutical preparations. Typical examples of prodrugs include organic phosphates or esters of alcohols or thioalcohols. See Remington's Pharmaceutical Sciences, 16th Ed., A. Osol, Ed. (1980), the disclosure of which is incorporated by reference herein.
Prodrugs are biologically inert or substantially inactive forms of the parent or active compound. The rate of release of the active drug, i.e. the rate of hydrolysis, is influenced by several factors but especially by the type of bond joining the parent drug to the modifier. Care must be taken to avoid preparing prodrugs which are eliminated through the kidney or reticular endothelial system, etc. before a sufficient amount of hydrolysis of the parent compound occurs.
Incorporating a polymer as part of a prodrug system has been suggested to increase the circulating life of a drug. However, it has been determined that when only one or two polymers of less than about 10,000 daltons are conjugated to certain biologically active substances such as alkaloid compounds, the resulting conjugates are rapidly eliminated in vivo, especially if a somewhat hydrolysis-resistant linkage is used. In fact, such conjugates can be so rapidly cleared from the body that even if a hydrolysis-prone ester linkage is used, not enough of the parent molecule is regenerated in vivo to be therapeutic.
Paullones are often poorly water soluble and are examples of substances which would benefit from PEG prodrug technology.
Attempts to increase the antiproliferative activity of the paullones has been reported. See Kunick et al., 2-Substituted Paullones. CDK1/Cyclin B-Inhibiting Property and In Vitro Antiproliferative Activity, Bioorganic & Medicinal Chemistry Letters, 10: 567-569, 2000. However, the study concentrates on substitution at the 2 position of 9-trifluoromethyl-paullones specifically with groups such as cyano, and carbon chain esters and ethers of varying length and saturation. The study does not solve the problem of maintaining CDK activity while increasing antiproliferative activity or improving the solubility of paullone analogs.
Thus, there still exists a need for derivatized heteroaromatic amine-containing compounds, for example, indole-containing compounds such as paullones, that exhibit potent preferential CDK inhibition combined with high antiproliferative activity. The present invention addresses this need.